1. Field of the Invention
The present invention relates to oscillators within integrated chips or circuits within communication devices, and, more particularly, the present invention relates to an oscillator having three stages, or phase shift circuits, in a cross-coupled configuration for use in a communication device, such as a wireless device.
2. Description of the Related Art
The use of wireless communications for in-home and in-building networks and direct communications is increasing. In conventional communication systems, data may be modulated onto at least one radio frequency (RF) and transmitted. For example, a transceiver may receive the RF modulated signal and demodulates the signal to recapture the data. In wireless applications, the data is modulated and transmitted over a wireless network to a location, or user equipment. The wireless device or user equipment receives the transmitted signal and demodulates it.
Regardless of the communication system or device, a transceiver may include an antenna, a filtering section, a low noise amplifier, an intermediate (IF) stage and a modulator/demodulator. An example is discussed as a receiver, as follows. The antenna receives RF modulated signals and provides them to the filtering section. The filtering section then passes the RF signals of interest to the low noise amplifier. The low noise amplifier may amplify the received RF signals of interest, and provide the amplified signals to the IF stage. The IF stage may include one or more local oscillators, mixers, or adders to step-down the frequency of the RF signals to an intermediate frequency signal, or to base-band signals. The IF stage provides the IF, or base-band signals, to the demodulator. Depending upon the particular protocol, algorithm or method, the demodulator of the example may demodulate the signals to recapture the transmitted data.
Components within the receiver may use an output signal from local oscillators. Oscillators seek to output signals having a specific frequency desired by the communication device or system. Once an oscillator reaches the specified frequency, the oscillator may lock onto the frequency. If the oscillator does not output a signal having the specified frequency, then the oscillator may be adjusted via feedback or other means until the specified frequency is achieved.
Ring oscillators may be used to provide an output signal having a desired frequency. Ring oscillators may include a plurality of stages or phase shift circuits, each one having a delay. The stages also can be referred to as delay cells. Each stage may have a specified phase shift and an overall phase shift within an oscillator of 360 degrees, or 360°. By having two or more stages, a ring oscillator may generate increased noise as well as introduce phase shift errors. These actions degrade the output signal, prevent the oscillator from reaching a desired frequency, and produce an inadequate frequency range for oscillation applications. Further, each stage of the oscillators may increase delay in transferring the output signal to the demodulator.
In addition, oscillators may use a current control implementing a voltage-to-current converter that converts a voltage control signal to a current signal, which in turn controls the oscillator and its resulting output signal. In other words, a control voltage is supplied to the converter that outputs a current control signal to the oscillator. The added component of the converter may increase noise in this particular oscillator.